JP2005280459A - Run flat tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a run flat tire improved in a run flat travel distance while suppressing significant degradation of riding comfort even when the tire becomes flat because of blowout or the like. <P>SOLUTION: The run flat tire 1 is provided with: a carcass 6; and a side reinforcing rubber layer 9 arranged on an inner side surface and in a side wall region of the carcass 6, and formed in an approximately crescent shape in cross section. The side reinforcing rubber layer 9 includes an inner side rubber part 9A arranged on an inner side of a tire axial direction with JISA hardness 70-95°, and an outer side rubber part 9B arranged on an outer side of the tire axial direction with the JISA hardness smaller than that of the inner side rubber part 9A, and 60-75°. The outer side rubber part 9B contains staple fibers f of which a longitudinal direction is substantially oriented along a radial direction. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a run-flat tire capable of safely and continuously running over a relatively long distance even when puncturing.

  Conventionally, various run-flat tires have been proposed that can safely and continuously travel a certain distance at a relatively high speed even when tire air is removed due to puncture or the like. In these various run-flat tires, a side reinforcing rubber layer having a substantially crescent-shaped cross section is provided in the sidewall portion, and after the air escapes, the sidewall portion including the side reinforcing rubber layer is the tire. Will support the load. Conventionally, various improvements have been made in order to further increase the distance traveled in a puncture state (hereinafter, such travel may be referred to as “run-flat travel”).

  For example, by increasing the size and hardness of the side reinforcement rubber layer and further increasing the rigidity of the carcass cord material, the amount of vertical deflection of the tire during run-flat travel is reduced, and durability during run-flat travel is improved. It is illustrated. However, these methods have a drawback in that the longitudinal spring of the tire is excessively raised, resulting in a significant deterioration in riding comfort. Patent documents related to run-flat tires include the following.

JP 2001-322410 A

  The present invention has been devised in view of the above problems. An inner rubber portion in which a side reinforcing rubber layer is disposed on the inner side in the tire axial direction and has a JISA hardness of 70 to 95 °, and the tire. An outer rubber portion that is arranged on the outer side in the axial direction and has a JISA hardness smaller than that of the inner rubber portion and 60 to 75 °, and the longitudinal direction of the outer rubber portion is substantially along the radial direction. It is an object of the present invention to provide a run-flat tire that can improve the run-flat mileage while suppressing a significant deterioration in ride comfort, based on the inclusion of short fibers oriented in the direction.

  The invention according to claim 1 of the present invention has a carcass having a radial structure extending from the tread portion to the bead core of the bead portion through the sidewall portion, and a substantially crescent shape in cross section disposed on the inner side surface and the sidewall region of the carcass. A run-flat tire comprising a side reinforcing rubber layer, wherein the side reinforcing rubber layer is disposed on the inner side in the tire axial direction and has an JISA hardness of 70 to 95 (°), and the tire And an outer rubber portion having a JISA hardness smaller than that of the inner rubber portion and 60 to 75 (°), and the outer rubber portion has a longitudinal direction substantially in the radial direction. It is characterized by containing short fibers oriented along.

  In the invention according to claim 2, the side reinforcing rubber layer includes the inner rubber portion and the outer rubber portion, and the thickness of the inner rubber portion is the maximum at the maximum thickness position of the side reinforcing rubber layer. The run-flat tire according to claim 1, wherein the run-flat tire has a thickness of 30 to 70 (%).

  The invention according to claim 3 is characterized in that the short fibers are composed of organic short fibers having an average diameter of 0.5 to 5 (μm) and a fiber length of 50 to 1000 (μm). It is a run-flat tire.

  In the run flat tire of the present invention, the side reinforcing rubber layer is disposed on the inner side in the tire axial direction and has an inner rubber portion having a JISA hardness of 70 to 95 °, and is disposed on the outer side in the tire axial direction and has the JISA hardness. An outer rubber portion that is smaller than the inner rubber portion and has an angle of 60 to 75 ° is included. During run flat running, compressive stress mainly acts on the inner rubber part, and tensile stress mainly acts on the outer rubber part. For this reason, the inner rubber portion is made of a hard rubber having a large JISA hardness, thereby preventing the compression strain from being concentrated inside the side reinforcing rubber layer. On the other hand, the outer rubber part is made of rubber having a JISA hardness smaller than that of the inner rubber part, so that vibrations or impacts that are input from the road surface to the tire during normal driving are relaxed and absorbed. This prevents deterioration in ride comfort due to the use of the hard inner rubber part. In addition, the outer rubber portion includes short fibers whose longitudinal direction is substantially aligned along the radial direction. Therefore, the elastic modulus is high with respect to the direction of the tensile stress acting during run-flat travel, and the strain against the tensile stress is increased. Can be suppressed. By these synergistic effects, the run-flat tire of the present invention can improve the run-flat mileage while suppressing a significant deterioration in riding comfort.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view of the run-flat tire 1 of the present embodiment in a normal state, FIG. 2 is a cross-sectional view in which the internal pressure is zero and a normal load is applied, and FIG. Cross-sectional views are shown respectively. Unless otherwise specified, the dimensions of each part of the tire are the values in the normal state.

  Here, the “normal state” uniquely defines the posture of the tire and is a no-load state in which the rim is assembled to the normal rim J and the normal internal pressure is filled. The “regular rim” is a rim determined for each tire in the standard system including the standard on which the tire is based. For example, a standard rim for JATMA, “Design Rim” for TRA, and ETRTO If there is, “Measuring Rim”.

  Furthermore, “regular internal pressure” is the air pressure that each standard defines for each tire in the standard system including the standard on which the tire is based. The maximum air pressure is JATMA and the table “TIRE LOAD LIMITS AT” is TRA. Maximum value described in “VARIOUS COLD INFLATION PRESSURES”, “INFLATION PRESSURE” for ETRTO, but 180 kPa for tires for passenger cars. Furthermore, “regular load” is the load that each standard defines for each tire in the standard system including the standard on which the tire is based. The maximum load capacity is specified for JATMA, and the table “TIRE LOAD LIMITS” for TRA. If the maximum value described in "AT VARIOUS COLD INFLATION PRESSURES", ETRTO, "LOAD CAPACITY" is used, but if the tire is for a passenger car, the load is equivalent to 88% of the load.

  The run-flat tire 1 of the present embodiment includes a carcass 6 having a radial structure that extends from the tread portion 2 through the sidewall portion 3 to the bead core 5 of the bead portion 4, and the carcass 6 on the outer side in the tire radial direction and inside the tread portion 2. The arranged belt layer 7, the bead apex 8 that tapers outward from the outer surface in the radial direction of the tire of the bead core 5, and the substantially crescent-shaped cross section disposed on the inner side surface and the sidewall region of the carcass 6. And a side reinforcing rubber layer 9. An inner liner rubber 10 made of rubber that does not easily transmit air is disposed on the inner side in the tire axial direction of the side reinforcing rubber layer 9.

  In the present embodiment, the carcass 6 is formed from a single carcass ply 6A. The carcass ply 6A is formed by covering carcass cords arranged in parallel with a topping rubber, and organic fibers such as nylon, polyester, rayon, and aromatic polyamide are suitably used for the carcass cord. In the present embodiment, the carcass cord has a radial structure that is arranged at an angle of 80 to 90 degrees, more preferably 85 to 90 degrees with respect to the tire equator C.

  In the present example, the carcass ply 6A includes a main body portion 6a straddling a pair of bead cores 5 and 5 (only one of them is shown in the figure), a tire connected to both ends of the main body portion 6a and around the bead core 5. And a folded portion 6b which is folded back from the inner side in the axial direction to the outer side and extends along the outer surface in the tire axial direction of the bead apex 8. In this example, the turned-up portion 6b extends beyond the carcass maximum width point M outward in the tire radial direction.

  Specifically, the outer end 6be of the folded portion 6b of the carcass ply 6A extends inward in the tire radial direction of the belt layer 7. That is, the folded portion 6b terminates at a position beyond the outer end 7e of the belt layer 7 inward in the tire axial direction. Here, the outer end 7e of the belt layer 7 is the end of the widest belt ply. Such a carcass ply 6A can effectively reinforce the sidewall portion 3 with a small number of one. Further, since the carcass ply 6A can move the outer end 6be of the folded portion 6b having low durability away from the side wall portion 3 that is easily bent during puncturing, the carcass ply 6A suppresses damage such as separation from the outer end 6be. It also helps to increase durability. On the other hand, during puncturing, a large bending stress is generated even in the vicinity of the tire equatorial plane due to the bending deformation of the tread portion 2. From such a viewpoint, it is desirable that the tire axial length EW where the folded portion 6b and the belt layer 7 overlap is, for example, 5 mm or more, preferably 10 mm or more, more preferably 15 to 25 mm.

  The bead apex 8 extends in a tapered manner from the outer surface of the bead core 5 to the outer side in the tire radial direction, and is made of hard rubber having a JISA hardness of 65 to 95 degrees, more preferably about 70 to 95 degrees. Thereby, the bending rigidity of the bead part 4 is raised and the vertical bending of the tire 1 is suppressed. The height ha of the bead apex 8 from the bead base line BL in the radial direction of the tire is not particularly limited. However, if it is too small, the durability during run-flat running tends to decrease. There is a risk of causing an increase in driving performance and a significant deterioration in riding comfort. From such a viewpoint, the height ha of the bead apex 8 is desirably 10 to 45%, more preferably about 25 to 40% of the tire cross-section height H.

  The belt layer 7 is composed of two belt plies 7A and 7B in which a belt cord made of steel is inclined with respect to the tire equator C at, for example, about 10 to 35 ° in this example. The belt plies 7A and 7B are overlapped so that the belt cords cross each other. As a result, the belt layer 7 strongly tightens the carcass 6 to increase the rigidity of the tread portion 2 and exhibits the advantages of a radial tire. In addition to the steel material, a highly elastic organic fiber cord such as aramid or rayon can be used as necessary for the belt cord.

  In the pneumatic tire 1, a rim protector 11 that protrudes so as to cover the outer side in the tire radial direction of the rim flange JF of the rim J and extends continuously in the tire circumferential direction is provided on the bead portion 4. As shown in FIG. 3, the rim protector 11 according to the present embodiment has, in a meridional section including a tire shaft, a protruding surface portion 11 c that protrudes most outward in the tire axial direction, and an edge of the protruding surface portion 11 c on the inner side in the tire radial direction. Continuously extending radially inward in the tire radial direction, the inner sloped surface portion 11a continuous with the bead portion 4, and the outer surface of the protruding surface portion 11c extending radially outward in the tire radial direction and smoothly extending to the sidewall portion 3 It is a raised body surrounded by the slope 11b.

  The protruding surface portion 11c is preferably provided at a position slightly protruding outward in the tire axial direction from the outer end point JFb of the rim flange JF in the tire axial direction. This also helps to protect the rim flange JF from curbs during normal travel. Further, the inner slope portion 11a is smooth including an arc portion having a center on the outer side in the tire axial direction than the bead portion 4 and formed with a curvature radius R1 larger than the curvature radius of the outer peripheral surface JFa of the rim flange JF. It is formed with a concave surface. As shown in FIG. 2, such an inclined surface portion 11 a can be deformed so as to lean toward the outer peripheral surface of the rim flange JF without resistance during run-flat traveling, and helps to reduce the shearing force to the carcass 6. . Further, the outer slope portion 11b is also smoothly formed including an arc portion having a radius of curvature R2 centered on the outer side of the tire.

  As shown in FIG. 3, in the normal state, the slope portion 11a in the rim protector 11 is hardly in contact with the outer peripheral surface JFa of the rim flange JF. However, during the run-flat running as shown in FIG. 2, the slope portion 11a in the rim protector 11 is in close contact with the outer peripheral surface JFa of the rim flange JF in a wide range so as to cover it. Thereby, the amount of vertical deflection of a tire at the time of run flat running can be controlled effectively, and durability can be improved. Accordingly, for example, the thickness of the side reinforcing rubber layer 9 can be reduced to further reduce the size or weight.

  The side reinforcing rubber layer 9 of the present embodiment is formed in a substantially crescent shape in cross section as a whole by gradually reducing the thickness from the thick central portion 9a toward the inner end 9i and the outer end 9o in the tire radial direction. Yes. The inner end 9 i is located on the inner side in the tire radial direction than the outer end 8 T of the bead apex 8 and on the outer side in the tire radial direction than the bead core 5. Further, the outer end 9o of the side reinforcing rubber layer 9 extends to the inner cavity side of the tread portion 2 and is terminated at a position on the inner side in the tire axial direction from the outer end 7e of the belt layer 7. Such a side reinforcing rubber layer 9 can reinforce the rigidity of the tire in the entire region of the sidewall portion 3, and more effectively suppress the amount of vertical deflection during run-flat running.

  In the side reinforcing rubber layer 9, the arrangement length L in the tire radial direction between the inner end 9 i and the outer end 9 o shown in FIG. 1 is not particularly limited, but if the arrangement length L is too small, the run flat During traveling, it is difficult to obtain a smooth curved state of the sidewall portion 3 as shown in FIG. On the other hand, if the arrangement length L is too large, the riding comfort is remarkably deteriorated and the rim assembling performance tends to be deteriorated during the normal running in which the internal pressure is appropriately satisfied. From such a viewpoint, the arrangement length L of the side reinforcing rubber layer 9 is preferably 35 to 70%, more preferably about 40 to 65% of the tire cross-section height H.

  Further, the side reinforcing rubber layer 9 of the present embodiment includes an inner rubber portion 9A disposed on the inner side in the tire axial direction and having a JISA hardness of 70 to 95 °, and disposed on the outer side in the tire axial direction and having the JISA hardness of the above-mentioned. A short fiber having a two-layer structure with an outer rubber portion 9B that is smaller than the inner rubber portion 9A and at an angle of 60 to 75 °, and the outer rubber portion 9B has a longitudinal direction oriented substantially along the radial direction. f is included.

  As shown in FIG. 2, during run-flat running, compressive stress mainly acts on the inner rubber portion 9A, and tensile stress mainly acts on the outer rubber portion 9B. As in this embodiment, by increasing the JISA hardness of the inner rubber portion 9A, it is possible to effectively prevent the compressive strain from concentrating on the inner portion of the side reinforcing rubber layer 9 and to prevent thermal destruction. it can. Here, when the JISA hardness Hd1 of the inner rubber portion 9A is less than 70 °, compression strain is concentrated on the inner portion of the side reinforcing rubber layer 9 during run flat running, and premature thermal destruction is likely to occur. If the angle exceeds 95 °, the ride comfort during normal driving tends to deteriorate significantly. From this point of view, the JISA hardness Hd1 of the inner rubber portion 9A is particularly preferably 75 to 90 °.

  On the other hand, the outer rubber portion 9B is made of rubber having a JISA hardness smaller than that of the inner rubber portion 9A. This is useful for relaxing and absorbing the vibrations or impacts input from the road surface to the tire during normal driving when the internal pressure is properly satisfied by the outer rubber portion 9B. Therefore, the run-flat tire 1 can prevent the deterioration of riding comfort due to the use of the hard inner rubber part 9A by arranging the flexible outer rubber part 9B on the outer side.

  Here, when the JISA hardness Hd2 of the outer rubber portion 9B is less than 60 °, the outer portion of the side reinforcing rubber layer 9 becomes remarkably soft, and the necessary rigidity during run-flat running cannot be obtained. Conversely, if the JISA hardness Hd2 of the outer rubber part 9B exceeds 75 °, the vibration absorption effect during normal running cannot be obtained and the riding comfort is deteriorated. From this point of view, the JISA hardness Hd2 of the outer rubber portion 9B is particularly preferably 60 to 70 °.

  Further, the difference (Hd1−Hd2) between the JISA hardness Hd1 of the inner rubber portion 9A and the JISA hardness Hd2 of the outer rubber portion 9B is not particularly limited, but is preferably 5 to 30 °, more preferably 10 to 25. It is desirable to set to °. When the difference in the JISA hardness (Hd1−Hd2) is limited to the above range, it is possible to prevent the occurrence of a large rigidity step at the interface between the rubber parts 9A and 9B, and to improve the run-flat durability performance and ride comfort. The improvement effect can be improved with a better balance.

  The interface S between the inner rubber portion 9A and the outer rubber portion 9B extends continuously from the inner end 9i to the outer end 9o of the side reinforcing rubber layer 9. That is, the side reinforcing rubber layer 9 of the present embodiment includes the inner rubber portion 9A and the outer rubber portion 9B in a substantially full length region. Such a side reinforcing rubber layer 9 can exhibit the above-described action over a wide range of the sidewall portion 3, and can ensure smooth deflection of the sidewall portion 3 even during run-flat travel.

  The outer rubber portion 9B includes short fibers f whose longitudinal direction is substantially aligned along the radial direction. In this embodiment, no short fibers are blended in the inner rubber portion 9A. In the present specification, the “radial direction” means a direction in which the carcass cord of the carcass ply 6 </ b> A extends, and this is different at each position of the sidewall portion. Further, the fact that the longitudinal direction of the short fibers f is oriented substantially along the radial direction means that the longitudinal direction of 90% or more of the short fibers f contained in the outer rubber portion 9B is ± 20 with respect to the radial direction. It is oriented in the angle range of °.

  Although the short fiber f mix | blended with the outer side rubber part 9B is not specifically limited, The nonmetallic fiber excellent in adhesiveness with rubber | gum is preferable. Specifically, organic short fibers such as nylon, polyester, aramid, rayon, vinylon, aramid, cotton, cellulose resin, and crystalline polybutadiene are suitable, but other inorganic short fibers such as boron, glass fiber, and carbon fiber are also suitable. Fiber may be used. Particularly preferably, an aramid short fiber is particularly preferable in order to further improve the run-flat durability. Moreover, a short fiber can be used 1 type or in mixture of 2 or more types. Further, the short fiber f may be subjected to a surface treatment or the like necessary for improving the adhesiveness with the rubber substrate.

  The average diameter and / or fiber length of the short fibers f are not particularly limited, but preferably the average diameter is 0.5 to 5 μm and the fiber length is 50 to 1000 μm. When the average diameter is less than 0.5 μm or the fiber length is less than 50 μm, there is a tendency that the effect of improving the elastic modulus in the radial direction cannot be sufficiently exhibited in the outer rubber portion 9B. If the fiber length is greater than 1000 μm, the adhesiveness between the short fibers f and the rubber decreases.

  In particular, in the case of the short fiber f having a long fiber length, the length of the bond with the rubber increases in the longitudinal direction, and therefore, fine peeling is likely to occur due to the shearing force of the bond interface generated during the tensile deformation during the run-flat running. This tends to grow due to the effects of heat and periodic strain during running, leading to early breakage of the side reinforcing rubber layer 9. From such a viewpoint, it is particularly preferable that the average diameter of the short fibers f is 0.5 to 2 μm and the fiber length is 50 to 500 μm. The aspect ratio of the short fiber f (value obtained by dividing the fiber diameter by the fiber length) is not particularly limited, but is preferably 0.2 to 4, more preferably about 0.5 to 2.

  In the outer rubber part 9B, for example, it is desirable that 10 to 30 parts by weight, more preferably 15 to 25 parts by weight of the short fiber f is blended with respect to 100 parts by weight of the rubber base material. When the blending amount of the short fibers is less than 10 parts by weight, the elastic modulus in the radial direction of the outer rubber part 9B cannot be effectively increased, and as a result, the effect of reducing the tensile strain of the sidewall part 3 is sufficiently obtained. There is a tendency not to be able to. On the other hand, if the blending amount of the short fibers f exceeds 30 parts by weight, the adhesiveness and crack resistance as a rubber material are remarkably lowered, so that the durability is easily impaired.

  The rubber base material used for the inner rubber portion 9A and / or the outer rubber portion 9B is not particularly limited, but is preferably a diene rubber, more specifically natural rubber, isoprene rubber, styrene butadiene rubber, butadiene rubber, chloroprene. Rubber and acrylonitrile butadiene rubber are desirable. Needless to say, these may be used alone or in combination of two or more.

  The method for forming the outer rubber portion 9B is not particularly limited. For example, as shown in FIG. 4A, the short fiber f is rolled in the extrusion direction by rolling a rubber material containing short fibers with calendar rolls r1 and r2. First, a rubber sheet G oriented in the longitudinal direction is molded. Then, the rubber sheet G is cut at right angles to the extrusion direction to obtain cut rubber pieces G1, G2,..., And this is laminated as shown in FIG. And the outer rubber part 9B which can orient the longitudinal direction of the short fiber f to radial direction can be formed. Further, as shown in FIG. 4C, the rubber sheet G can be similarly formed by folding and laminating.

  In the outer rubber part 9B, only the orthogonal anisotropy, that is, the complex elastic modulus E * r in the radial direction is remarkably increased by the orientation of the short fibers f. The radial direction is equal to the direction of the tensile load acting on the outer side of the side reinforcing rubber layer 9 during run flat running. Accordingly, the outer rubber portion 9B can remarkably resist the tensile load during run-flat running without impairing the ride comfort, and can suppress the occurrence of large tensile strain.

  As a particularly preferable aspect of the outer rubber portion 9B, by adjusting the material and blending amount of the above-described short fiber f, the radial elastic modulus E * r and the tire circumferential elastic modulus E * c The elastic modulus ratio represented by the ratio (E * r / E * c) is desirably 2.0 or more, more preferably 2.5 or more, and the upper limit thereof is 10 or less, more preferably 6 or less. Is desirable. The complex elastic moduli E * r and E * c were measured using a viscoelastic spectrometer “VES F-3 type” manufactured by Iwamoto Seisakusho, measuring temperature 70 ° C., frequency 10 Hz, initial elongation strain 10%, single amplitude. The value measured at 1%. The measurement sample can be prepared by dismantling the tire, cutting out from the part in a size of 4 mm in width, 30 mm in length, and 1 mm in thickness and smoothing by buffing the surface irregularities.

  Moreover, as for the side reinforcement rubber layer 9, it is desirable to set appropriately each thickness of 9 A of inner side rubber parts, and the outer rubber part 9B. Specifically, as shown in FIG. 3, at the position of the maximum thickness t of the side reinforcing rubber layer 9, the thickness ti of the inner rubber portion 9A is 30 to 70% of the maximum thickness t, more preferably It is desirable that it is 50 to 60%. If the thickness ti of the inner rubber portion 9A is less than 30%, the compression resistance required for run-flat running tends to be insufficient. Conversely, if it exceeds 70%, the riding comfort during normal running tends to deteriorate. There is.

  The maximum thickness t of the side reinforcing rubber layer 9 is the largest portion of the thicknesses measured in the direction perpendicular to the center line of the thickness of the side reinforcing rubber layer 9, and is preferably in the case of a tire for a passenger car. Is preferably 5 to 14 mm, more preferably 7 to 11 mm. Further, when the side reinforcing rubber layer 9 includes a portion having a maximum thickness t and continuing in a constant length in the tire radial direction, the maximum thickness position is determined by an intermediate portion of the length.

  As described above, the run-flat tire 1 of the present embodiment has the vertical deflection of the tire during run-flat running without causing a significant deterioration in ride comfort due to the synergistic action of the inner rubber portion 9A and the outer rubber portion 9B. The amount can be suppressed, and the run-flat mileage can be increased as compared with the prior art.

FIG. 5 shows another embodiment of the run flat tire 1 of the present invention.
In the present embodiment, the outer rubber portion 9B includes a first outer rubber portion 9B1 and a second outer rubber portion 9B2 having different complex elastic modulus E * r in the radial direction. In this embodiment, the first outer rubber portion 9B1 is disposed on the outer side in contact with the inner rubber portion 9A, and the second outer rubber portion 9B2 is further on the outer side in the tire axial direction of the first outer rubber portion 9B1. It is arranged in.

  When the side reinforcing rubber layer 9 is subjected to bending deformation during run flat running, the outer side of the outer rubber portion 9B in the tire axial direction moves away from the bending neutral line, so that a larger tensile stress acts. Therefore, in this embodiment, the complex elastic modulus E * r in the radial direction of the outer rubber portion 9B is associated with the magnitude of the applied stress. That is, a rubber material having a larger complex elastic modulus E * r in the radial direction than that of the first outer rubber portion 9B1 is used for the second outer rubber portion 9B2.

  In the first and second outer rubber portions 9B1 and 9B2, the complex elastic modulus E * r in the radial direction is determined by the blending amount of the short fibers f, the material of the short fibers, the aspect ratio of the short fibers, and / or the rubber sheet molding. It can be adjusted by making at least one of the rolling times different. In this embodiment, the complex elastic modulus E in the radial direction is set by making the blending amount of the short fibers f of the second outer rubber portion 9B2 larger than the blending amount of the short fibers f of the first outer rubber portion 9B1. * Examples with large r Such a side reinforcing rubber layer 9 changes the complex elastic modulus E * r in the radial direction of the outer rubber portion 9B in relation to the tensile stress, so that the distortion in each portion is made uniform and more efficient. Tensile resistance can be improved. This is useful for improving durability and downsizing of the outer rubber portion 9B. Particularly preferably, the ratio of the complex elastic modulus E * r1 in the radial direction of the first outer rubber part 9B1 to the complex elastic modulus E * r2 in the radial direction of the second outer rubber part 9B2 (E * r2 / E * r1) is preferably about 3 to 5. The outer rubber portion 9B may be composed of a plurality of layers of three or more layers having different complex elastic modulus E * r in the radial direction.

  Further, as indicated by a virtual line V in FIG. 5, the inner rubber portion 9A can also be formed using two or more kinds (two kinds in this example) of rubber materials having different JISA hardness. Even in this case, since the compressive stress increases toward the inner side in the tire axial direction of the side reinforcing rubber layer 9, it is desirable to increase the JISA hardness toward the inner rubber.

  In order to confirm the effects of the present invention, a plurality of types of run flat tires of size “245 / 40R18” based on the specifications in Table 1 were prototyped and evaluated for ride comfort performance and run flat durability performance. Each tire was the same except for the parameters shown in Table 1. The test method is as follows.

<Ride comfort>
Each test tire is mounted on a rim of 18 x 8 JJ and has an internal pressure of 230 kPa and mounted on four wheels of a domestic FR vehicle with a displacement of 3000 cm ³ , and a stepped road on the dry asphalt road surface, Belgian road (under one driver) Cobblestone road surface), Bitzmann road (road surface covered with pebbles), etc., sensory evaluation is performed with respect to ruggedness, push-up, and damping, and is displayed as an index with Comparative Example 1 being 100. The higher the value, the better .

<Run flat durability performance>
Each test tire was assembled on a regular rim (18 x 8 JJ) with the valve core removed, and was run on the drum tester at a speed of 90 km / h and a longitudinal load of 5.74 kN with zero internal pressure until the tire was destroyed. The mileage was measured. The results are indicated by an index with Comparative Example 1 being 100, and the larger the value, the better.
Table 1 shows the test results.

  As a result of the test, it can be confirmed that the tire of the example improves the ride comfort and the run-flat durability performance in a well-balanced manner as compared with the comparative example.

It is sectional drawing of the run flat tire which shows embodiment of this invention. It is sectional drawing of the run flat state. It is a fragmentary sectional view which expands and shows the bead part of FIG. (A), (B) and (C) are schematic diagrams for explaining a method of manufacturing the outer rubber portion. It is a fragmentary sectional view of the run flat tire which shows other embodiments of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Run flat tire 2 Tread part 3 Side wall part 4 Bead part 5 Bead core 6 Carcass 7 Belt layer 9 Side reinforcement rubber layer 9A Inner rubber part 9B Outer rubber part 9i Inner end 9o of side reinforcement rubber layer Outer end of side reinforcement rubber layer 9a Central part of side reinforcing rubber layer f Short fiber

Claims (3)

A run-flat tire comprising a radial carcass extending from the tread portion through the sidewall portion to the bead core of the bead portion, and a side reinforcing rubber layer having a substantially crescent cross section disposed on the inner side surface and the sidewall region of the carcass. Because
The side reinforcing rubber layer is disposed on the inner side in the tire axial direction and has an inner rubber portion having a JISA hardness of 70 to 95 (°),
An outer rubber portion that is arranged on the outer side in the tire axial direction and has a JISA hardness smaller than that of the inner rubber portion and 60 to 75 (°), and
The outer rubber portion includes a short fiber whose longitudinal direction is oriented substantially along the radial direction.   The side reinforcing rubber layer includes the inner rubber portion and the outer rubber portion, and the thickness of the inner rubber portion is 30 to 70 (%) of the maximum thickness at the maximum thickness position of the side reinforcing rubber layer. The run flat tire according to claim 1, wherein   The run-flat tire according to claim 1, wherein the short fibers are organic short fibers having an average diameter of 0.5 to 5 (μm) and a fiber length of 50 to 1000 (μm).

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